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Thursday, November 26, 2015

Calling 3rd Party Python Modules in Blender Scripts

Introduction

This costed me nerves....
Yesterday I had the idea of connecting a Blender 2.76b via a Blender plugin - which still needs to be written... - to a SQL Server database installation where I keep geometric data of some objects. Furthermore I am working in a windows environment using a Anaconda python installation, which I normally run with Python 2.7.6.
The python weapon of choice to connect to a database is the module PYODBC which offers convenient functions to access databases. Unfortunately, this module is not available in Blender's bundled Python installation. I did not manage to install pyodbc within the context of Blender's bundled python

So this is where my odysee started. I had the following challenges to solve:

Create a Python environment compatible woth Blender 2.76b

Turn Blender's python environment to the environment with pydbc

Creating an Independent Python Environment

As I said I am using the Anaconda IDE. My first approach was to install plain Python 3.4.2 (required for Blender 2.76) from python.org in parallel to Anaconda. Installation and stuff wen fine, but quickly I ran into the issue that I wanted to install the pyodbc package on top of the standard installation and this was not possible as this installation requires a working VS2013 (?) environment to compile the sources. This is where I went back to Anaconda.

In Anaconda it is possible to create version dependent python environments in parallel to the intitial installation using the command

conda create -n <environment name> python=<version number>

The new environment can be found at the path:

..\<Anaconda root path>\envs\<environment name>

To activate the environment call in the command line:

activate <environment name>

So whatever you have to change to adjust your Python installation for Blender needs to be done in the environment with the right version number for Blender. The following steps assume that you activated an environment with this right version.
In Anaconda modules like pyodbc can be installed very easily without the need for external tools and compilers. This is done by calling (in this example I am installing pyodbc):

conda install pyodbc

The conda command fetches all the required sources from the internet, compiles them if needed and adjusts the environment so they can be used.
3rd party modules (like pyodbc) are stored at a path

..\<Anaconda root path>\envs\<environment name>\Lib\site-packages

This is where Blender needs to look for the 3rd party module.

Telling Blender where to Find Things

I tried a couple of things to tell Blender where to look for pyodbc, including setting the PYTHONPATH variable following this blog post, deleting Blender's Python, etc. However, all of these approaches were very cumbersome and led to negative interferences between Blender and Anaconda - meaning either of these did not work.
Finally I found a solution which seems to me quite elegant: I don't do any system-related settings like PYTHONPATH and stuff and do everything need in my script.
I simple check if the path to pyodbc (or any other 3rd party module) is already included in the sys.path varialble of Python. If this is not the case I append the required path and import the module after having registered the path: